I have my students working with both at the moment. I like the 12 step's octave control and single and multi key modes. Re: Per's concern, I find you can improve responsiveness of the controller by tweaking the global sensitivity. This is a good approach to get the most out of the tilt function, for example. See p. 16 in the manual. The softstep is great for the usual parametric control: toggle, pressure, XY.
Also this comparison table may be of use: http://www.keithmcmillen.com/support/stepcomparison/
If anyone is interested in purchasing, I rep in NJ/NY. Get in touch, off list.